Patent GB-754652-A (GB)
Title: Selection system for electrical circuits or equipments
IPC: H04Q1/18
Filed: 1950-01-16
Abstract: 754,652. Automatic exchange systems. STANDARD TELEPHONES & CABLES, Ltd. Jan. 16, 1950 [June 30, 1949], No. 1093/50. Class 40 (4). In a selector switch circuit a series of different test signals are applied in turn to a common test circuit, each signal relating to a different outlet and by its identity defining the condition and identity of the outlet with which it is associated. As described, these signals are potential pulses occurring in different time positions in a recurrent cycle of time positions, the time position of a pulse defining the identity and condition of the outlet concerned. These pulses are produced by scanning the outlets, using a scanning circuit consisting of a number of rectifier gates which enables the paths between the outlets and the common test circuit in turn cyclically. Details. The scanning system is basically the same as that of Specification 700,088 but the Pd sources (not shown) instead of characterizing the groups of outlets of a group selector are used firstly to indicate the condition of the outlets, i.e. local busy, toll busy or free; and secondly to characterize P.B.X. groups in the control of P.B.X. hunting. For this purpose source Pd4 is allocated to free single lines, Pd1 to local busy lines, Pd2 to toll busy lines, and Pd5-10 to P.B.X. groups. Selection of single line. It is assumed that the register-controller has recorded the tens and units digits and has effected the connection of one source in each of the groups Pc, Pb, Pa to the grids of Va2, Va4 and Va3 respectively (Fig. 1B). The impulses reverted from the control circuit when idle lines are scanned are applied to the grid of Va1 as in Specification 700,088. Each impulse received on a grid renders the corresponding tube conductive and the cathode goes positive. The two twin triodes Va1, Va2 ; Va3, Va4 have their cathodes interconnected through rectifiers Rc1, Rc2 ; Rc3, Rc4 and all connected in parallel to the grid of Vo2 (Fig. 1A). As long as one or more of the cathodes of tubes Va1-4 are negative the impulses from source d3 which are applied to the grid of Vo2 are absorbed in a 20K resistance, but when impulses are simultaneously applied to the grids of Va1-Va4 the corresponding impulse d3 renders Vo2 conductive. This triggers Vo1 and an impulse is sent over the C wire to the final selector. This impulse also fires Via in the register-controller and the resulting operation of Ot connects test relay T to the A wire. Registration of identity of selected outlet and operation of the vertical magnet of the selector takes place as in Specification 700,088. Checking class-of-outlet. This is checked in the manner described in the above Specification and the relevant horizontal magnet and servomagnet are operated to complete the selection. Called line busy. As soon as a line is engaged the source Pd4 connected to the individual resistance Rg (Fig. 5) is prevented from supplying impulses to tube SVA3 (Fig. 4), impulses from either Pd1 or Pd2, according to whether the line is local busy or toll busy respectively, being supplied in their place. Source Pd1 is connected to wire D of the desired line by the link circuit employed in the local call, and Pd2 by the inlet circuit used in the toll call. Thus when Pd4 sends an impulse it results in current flow to the source Pd1 or Pd2 and is not effective owing to the voltage drop in Rg. No impulse is reverted for a busy single line during the pulse period of Pd4 (viz. time units 361- 480) but an impulse is reverted during that of Pd1 or Pd2 (viz. during time units 1-120 or 121-240 respectively). In the register-controller tube Vo2 fires in response to this impulse (in either case) and the regenerated impulse is sent forward over the C wire. If this impulse is in the first period 1-120, tube Vabu controlled by source Rd1 fires to record the local busy condition, whereas if it is in the second period another tube (not shown) controlled by Rd2 fires. The class of the wanted line is then signalled to the register-controller as for a free line. Assuming the line is a single line, relays Oa and Oe (Fig. 1A) are energized. The partial connection is released and busy tone reverted. Selection of line in a P.B.X. group. If the wanted line is one of a P.B.X. group comprising lines with non-consecutive numbers, its resistance Rg is connected to that one of the sources Pd5 to Pd10 which characterizes the group. Provided the line is free an impulse is reverted in the relevant time position in the period determined by the source Pd and selection proceeds as for a single line. When the line is engaged, the Pd5 to Pd10 impulse is suppressed and Pd1 or Pd2 replaces it as for a single line. Operation is the same up to the moment when the class-of-line is checked. If the line is one which does not correspond to the common call number of the P.B.X. group the class-of-line indication is as for a single line and busy tone is reverted as before. P.B.X. hunting. However, if the line is a first line of a P.B.X. group the indication given is " first line of nth P.B.X. group ", viz. an impulse is sent in one of the time units 78, 84, 96, 102, 108 or 114 according to the P.B.X. group concerned. On the reception of this impulse in the register-controller, Si and Ot come up and T is connected to the A wire as before. GC in the common control circuit is operated and the completion of the double test brings up Dt followed by Cs. All operated class-of-line relays Oa . . . Oh are released, Or pulls up, and Ot relapses. The grids of Va2, Va3, Va4 are thus connected to ground, Pa1, and ground respectively so that only impulses characterizing the class-of-line (Pal) can be effective. The impulse characterizing the first line of the first P.B.X. group operates relays Oc, Og and with Bu up Ph is energized. Tube Via is restored, Si is released and reconnected to Vib, and Bu falls off. The grids of Va2, Va3, Va4 are now connected to Pd5, Pa2 . . . 6 in parallel, and ground respectively. The A wire circuit is opened and GC (Fig. 4), T, Dt, Cs and Or (Fig. 1) fall away. GD or GE and the operated vertical magnet release and GB reoperates so that impulses are again reverted for all idle lines. The register-controller can respond only to line identification impulses during periods of emission of Pa2 . . . Pa6 and Pd5. Thus the transmission of line identification impulses during the periods of emission of Pd5, Pd6 during the first test are not recorded, the transmission of class-of-line impulses by means of Pa, Pb, Pc through the 20 class-of-line wires (Fig. 5) indicates the desired P.B.X. group and the final selector then operates in the same manner as the group selector of Specification 700,088 to select the first idle line in the group transmitting line identification impulses in the period Pd allocated to the P.B.X. group in question. When an impulse arrives from the final selector on the grid of Va1 during period Pd5, for example, an impulse is produced by Vo1 and returned to the common control circuit to record the identity of the selected line. This impulse also operates tube Vib and relay Si, and the register-controlled then acts as for a call to a single free line. The class-of-line indication for a P.B.X. line other than the first is that of a single line viz. an impulse in time unit No. 6 over wire COL No. 1 (Fig. 5). Small consecutively numbered P.B.X. groups. These may be provided by jumpering a classof-line indication for all lines except the last over wire COL No. 12 (time unit No. 72) while the last line is connected as for a single line to COL No. 1. All the line numbers in a group differ only in the units digit. A call is routed to any free line of such a group exactly as described for a free single line. P.B.X. hunting. If a called line other than the last of the group is busy, the procedure is the same as described above up to the checking of the class-of-line. When the busy condition is signalled Bu and Si come up as before followed by Ot, T, Dt and Or whereupon Ot falls away. The grids of Va2-4 are connected up as before for receiving class-of-line impulses and in this case Oc, Of are operated, and Ph follows. The subsequent operation of Ia causes the device which has registered the units digit to advance one step so as to change the Pa source to that characterizing the next outlet. Lm pulls up and Ph releases Bu whereupon Ph itself relapses followed by T, Dt (Fig. 1B) and GC (Fig. 4). GB reoperates and revertive impulses are again sent, the grids of Va2-Va4 being again connected to the relevant Pc, Pa and Pb sources. The next line is thus tested in the same manner and so on until the last line is reached. This is treated as a single line. Specifications 754,655 and 754,702 are referred to.