Patent GB-728265-A (GB)
Title: Circuit arrangement for telecommunication installations
IPC: H04Q3/00
Filed: 1953-03-13
Abstract: 728,265. Automatic exchange systems. SIEMENS & HALSKE AKT.-GES. March 13, 1953 [March 14, 1952; May 16, 1952], No. 7026/53. Class 40 (4). In a circuit in which free and busy outlets of a switch are distinguished by different D.C. potentials, the change in test current through the primary winding of a transformer when a free outlet is encountered induces a voltage surge in the secondary winding of sufficient magnitude to stop the switch. In one arrangement, Fig. 1, a relay C (not shown) pulls up when a preselector VW is taken into use and when the test wiper c reaches a free outlet, the potential thereon (- 60 volts) causes a test current to flow through the primary of transformer TR of sufficient magnitude to effect triggering of a valve R by the induced voltage surge in the secondary winding. Relay P in the anode circuit then pulls up over winding I, stops the preselector and switches through the speech circuit. This relay also disables the valve but remains held by a second winding II. Due to voltage drops produced by the test current in the primary winding and in a resistor Wi associated with the c outlet, the outlet potential changes to a value (- 6 volts) indicative of a busy condition. Busy outlets cannot be taken into use by another switch since the lowered potential reduces the test current, and the induced voltage is then insufficient to trigger a valve. A rectifier GL may be connected in series with the primary winding so that a greater divergence in test currents arising at free and busy outlets is obtained due to its non-linear characteristic. In a second embodiment, Fig. 2, relay AN is pulled up by relay C (not shown) when the preselector is taken into use and completes a circuit for drive magnets M1, M2 which are alternately energized over mechanically controlled contacts 4m, 5m. When a free outlet is found, the characterising potential (- 60 volts) establishes a current through the primary winding of a transformer T, and the resultant induced voltage surge in secondary winding W2 fires a double-anode gas tube R over biased grid G1 (- 80 volts) except when a disabling potential (- 70 volts) is present on a grid G2. The disabling potential is neutralized periodically by voltages induced in the second windings II of M1, M2 each time a drive magnet is energized so that the available testing time at each outlet is restricted. Firing of the tube causes the switch to stop by simultaneous excitation of the drive magnets over the anode circuits. In the cathode circuit the current pulls up relay P and induces a voltage pulse in the transformer primary winding over a secondary winding W3 which temporarily busies the outlet to other switches during the response time of the relay. When relay P operates, a permanent busy marking (- 2 to - 7 volts) is applied to the outlet through a holding winding II. The gas tube is also extinguished and relay AN falls back and disconnects the drive magnets. The arrangement also includes a rectifier in the test circuit which prevents the flow of test current in the reverse direction and consequential undesired induced voltages, and a resistor W11 or a rectifier GL2 connected respectively in the primary or secondary circuits which extend the time period of the voltage surge. In a modification of Fig. 2, Fig. 3 (not shown), the additional transformer winding W3 is connected to an auxiliary anode of the gas tube to avoid the time delay produced by the inductive drive magnets M1 and M2.