Patent GB-1153214-A (GB)
Title: Automatic Telephone System
IPC: H04Q3/00
Filed: 1967-02-23
Abstract: 1,153,214. Automatic exchange systems. PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd. 23 Feb., 1967 [26 Feb., 1966], No. 8626/67. Heading H4K. A test position CM can obtain a connection to a line circuit LS in a manner such as not to operate the busy relay S at the line circuit, a calling condition simulated in the line circuit by means of a signal from the test position causing the exchange marker to connect the line circuit to a register in response to which connection the busy relay S operates. Line supervision is effected by interrogation of a magnetic core O in the line circuit; loop current in windings W 1 , W 2 , switching the core against normal bias in winding W 5 , and interrogation pulses to winding W 6  producing output in winding W 4  if the core is so switched. When a connection is made to the line circuit over the relay crosspoint switching network, operating current is normally supplied over marker contacts m 11  so that when the A stage crosspoint operates to 36 volts negative the S relay also operates in the line circuit, holding current in the path c-wire driving a winding W 3  on the line circuit core O. Thus the busy relay S disconnects the windings W 1 , W 2 , but with holding current in W 3  preserves output at W 4  to scanner interrogations on W 6 . If the test position CM wants a connection with LS it signals the marker over contacts cm 3  where discriminator K 0  conditions the marker to operate the path over the network with 46 volts negative from contacts m 12  so that potential across busy relay S is insufficient to operate S. Holding current over the c-wire, however, by switching core O in winding W 3  busies the line circuit to the scanner as is normal for a call termination. To remove this busy record 24 volts is connected to the b-wire from contacts cm 2  of CM, the resulting current in winding W 2  neutralizing the effect of holding current in W 3 . The core O is, therefore, switched by the first interrogation and found idle on subsequent interrogations. To establish a calling condition from LS the test station takes down its handset from TCM and consequent current in W 1 , W 2 , reswitches the core O. When the marker responds by connecting a register, the relay S operates in the normal manner and the set TCM can be employed to establish a connection from LS. A modified line circuit is shown in Fig. 2 where an additional core N enables the busy condition to be maintained to the scanner when the line circuit is released on the network side but the associated subscriber stays off-hook. Loop current is taken through a winding U 5  on core N but does not switch the core. Calling condition is signalled by output from W 4  to interrogation on W 6 ; interrogation of U 2  producing no output from U 4 . A connection to the network switches N with holding current on the c-wire through U 1 , the scanning circuits being such that coincidence of output from W 4  and U 4  results in switching pulses from the scanner to U 2 . When a connection has been set up from station CM the busy condition is removed by application of 24 volts to the bwire to neutralize holding current flux in cores O and N. Rectifier GLS removes loop resistor R 2  in this circuit. Loss of interrogation output from W 4  and U 4  clears down the recorded busy condition. A calling condition is then set up by earthing the a-wire over the network from contacts cm 4  so that core O switches to current in W 1  but core N remains unswitched.