GB1244396A - Improvements in or relating to telecommunications exchange systems - Google Patents

Abstract

1,244,396. Automatic exchange systems. SIEMENS A.G. 29 Sept., 1969 [30 Sept., 1968], No. 47754/69. Heading H4K. In a remote concentrator equipped with a remanent relay switching network, a calling subscriber is connected through to one of a plurality of free junctions under the control of a line-identifying counter which is controlled from the main exchange over a speech or control junction by bipolar pulses. At each step a transistor bridge circuit, which effectively (due to a contact chain of the counter) includes in one arm only that subscriber line indicated by the step, is caused to test the loop resistance via contacts of the line's cut-off relay (T). If this indicates a calling condition the next (opposite polarity) pulse from the parent exchange brings up a marking relay (M) pertaining to this subscriber instead of, as usual, stepping the counter. The pulses normally encounter a loop through the counter and its associated circuitry so that elimination of the return pulse when the marker relay operates is effective to identify the caller (on a similar counter) at the parent exchange. The next pulse restarts the counter which is then stepped on without further interruption by subsequent pulses until it reaches its last stage. Power for operating the counter relays (Z), the marker relays (M), the cut-off or busy relays (T) and the switching relays (K) is derived from capacitors that are charged by the bipolar pulses and discharged via transistor amplifiers through the relays during the pauses between pulses. Two transistor bridges (B1, B2) and two associated thyristors (Th1, Th2) are provided for responding to opposite polarity pulses thereby speeding the operation of the counter. The latter may be stepped by the pulses to a particular line when an incoming call is to be set-up. The system is said to be not susceptible to serial voltages (presumably earth currents) on the junctions.