Patent GB-824466-A (GB)
Title: Improvements in or relating to circuits for selecting the first member in a predetermined multi-stage sequence of members
IPC: G11C11/06
Filed: 1957-09-18
Abstract: 824,466. Automatic exchange apparatus. TELEFONAKTIEBOLAGET L.M. ERICSSON. Sept. 18, 1957 [Sept. 20, 1956], No. 29414/57. Class 40 (4). The first marked one of a number of circuits or groups of circuits arranged sequentially is selected by means of a chain connection of centre-tapped windings, each winding being on a magnetic core peculiar to a particular circuit or group of circuits and one end of the chain being connected to one potential pole while the circuits or groups are marked by connecting the centre tap of that circuit or pole to the other potential pole, current in one half of the winding then shifting flux in the core whereas if the centre tap was not so connected the halves of the centre tap winding would cancel one another. In Fig. 1 the centre-tapped windings P1 to Pn are connected to contacts kl to kn. When a contact 13 is made to connect positive battery to the windings capacitor 12 charges and current through the upper half winding of the first core marked in the sequence produces an output in secondary winding S1 to Sn to fire the appropriate gas discharge tube G1 to Gn which over lead L1 to Ln provides a controlling output. When one tube has fired, current through resistor 14 drops the trigger electrode voltages to provide lock-out. To prepare the circuit for a further selection contact 13 is broken and made. To prevent coupling between a first selected core and a marked core later in the sequence the windings and/or the connecting wires are given a resistance of anything up to 20 ohms. If one of the contacts k1 to kn becomes made permanently due to a fault, all subsequent circuits will be inaccessible. To avoid this the order of the sequence is reversed for each alternate selection by means of contact 18. In place of the gas-discharge tubes trigger circuits may be used comprising a transistor connected with the two windings of a relay to form a blocking oscillator, the relay locking up to an oscillation (see Fig. 2, not shown). Each contact k1 to kn may be replaced by a group of contacts in parallel the group being marked if any one contact of a group is made. In Fig. 3, the invention is applied to mark the column and row of an operated contact in a co-ordinate array of contacts kmn. For this purpose each core C1 to Cm carries the centre-tap windings of the contacts of a particular row which is marked by a circuit M1 to Mm operated by secondary winding S1 to Sm. The columns of windings associated with the contact columns are connected in series with column marking relays R1 to Rn and associated gas-discharge tubes A1 to An with their common lock-out circuit comprising tubes GA and GN. Supposing contact k12 is made. The cathode of A2 drops in voltage and fires but draws little current as high resistance 33 stands between the anode and voltage source Va. To protect the core C1 a small compensating current is drawn over high-resistance 31 in the other half of the core winding to contact k12. When A2 fires, a pulse over capacitor 34 fires GA which fires GN to modify current in the resistor chain 36, 37, 38, to lock out the idle tubes A1 to An. When GA conducts relay IR responds to connect tube A2 directly to potential Va and cause it to conduct fully thereby pulsing the core C1 to set the marker M1 and operating R2 which locks up. The lock-out circuit ensures that a relay R1 to Rn does not operate until lock-out is effective. In Fig. 4, the operated one of a co-ordinate array of contacts kmn is identified by means of an associated array of cores F with rectangular hysteresis loops. A pulse source PG steps a distributer 45 over a normally open gate 44 and cyclically interrogates the columns of series connected centre-tapped windings. Before a column is interrogated all the cores are set to one state by a common winding t. If contact k12 is made its core is turned over under interrogation and produces an output in row wire x1 to operate marker M1 of the set M1 to Mm. An output is also produced in the common winding t to operate a trigger circuit 43 to close the gate 44 and halt the distributer which therefore marks the column. A separate set of column windings may be provided to operate a set of column markers M<1>1 to M<1>n and each core may have a reset winding other than the winding t.