Patent GB-800657-A (GB)
Title: Improvements in or relating to subscribers' circuits for telephone exchange systems
IPC: B01D21/00
Filed: 1956-07-27
Abstract: 800,657. Automatic exchange systems. PHILIPS ELECTRICAL INDUSTRIES, Ltd. July 27, 1956 [July 30, 1955], No. 23294/56. Class 40 (4). To improve the transmission of dialled impulses in a system in which connections are established over gas discharge tubes, lines from a subscriber are connected to the primary windings of a transformer T, the subscriber's loop circuit being supplied with D.C. from a source BA1 and including a rectifier G in the D.C. path poled to pass current from the source BA1; a secondary winding on the transformer T being connected in series with the rectifier G, a resistor R3, a gas discharge tube B and an impedance L, across the terminals of a second D.C. source BA2 poled in opposition to the rectifier G which is shunted by a resistor R4. From the top of the secondary winding of transformer T multiple connections M1 are made connecting the subscriber's line circuit to a gas discharge tube such as B in each one of a number of connecting circuits VC. From the anode of each gas discharge tube B multiple connections M2 are made to the anodes of other discharge tubes at the connecting circuit, the cathodes of which are each connected to a subscriber's line circuit. A counting circuit TS has outlets U1-U5 connected to the ignition electrodes f of each of the discharge tubes B at the connecting circuit. When subscriber AB completes his loop circuit current passed by G through R2 drops the potential of the cathodes of all the tubes B in available connecting circuits VC and, as soon as one tube fires, say the tube shown, current from BA2 through R3 raises the potential of all the cathodes multiplied at M1 to mark the subscriber busy in all the connecting circuits. Current from BA2 through R7 drops the potential of all the anodes multiplied at M2 and marks the connecting circuit busy to incoming calls. In this condition of the circuit rectifier G passes 50 m/a. from BA1 and 10 m/a. in the opposite direction from BA2. When the loop circuit is broken during dialling, G ceases to conduct and the resistance of the cathode circuit of B is increased by the high resistance of R4 causing the anode potential to rise from 90 to 130 volts. The increase in voltage at the top of R7 is used to control the counter TS which steps once for each pulse and when at rest at the end of the impulse train the outlet of the counter corresponding to the digit dialled increases its potential to fire a second idle tube B connected to multiple M2, causing ringing current to be applied to the called subscriber's line by means not described. When the called subscriber replies by closing his loop circuit a talking path is completed over two transformers and two tubes B. A non-linear resistance X damps out the pulse received by the transformer T when the subscriber's loop is made. To release the connection the loop circuits are broken and means is provided to extinguish the discharge tubes. This means may be a relay bridge or may be a device, not described, operated by the continued interruption of a loop circuit but not dialling pulses; or, alternatively, the impulsing contacts may be shunted by a resistor so that the voltage on the anodes of tubes B does not increase as much during dialling as when the loop circuits are open circuit. Specification 707,760 is referred to.