Method of and circuit arrangement for evaluating the output signals of current flow detectors in telecommunication facilities
AssigneeU. S. Philips Corporation
InventorManfred Schmidt
Life of this patent
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Abstract
The flow of direct current and/or ringing alternating current in a telephone line subscriber loop is detected by means of current flow detectors. The output signals produced by the current flow detectors are applied to an evaluation circuit, the zero-crossings of the ringing alternating current being used to determine whether a ringing alternating current has been superimposed on the loop direct current. In order to increase the reliability of the evaluation and to detect noise voltages coupled into the subscriber-loop, the durations of positive and negative half-waves of the loop current are measured and the evaluation is effected by comparing the sum and the ratios of the measured values relative to a presettable threshold.
Claims5
A method of evaluating the output signals of subscriber line current flow detectors in a telephone exchange, such exchange including at least one current flow detector (SDS) connected to one of a pair of subscriber lines and which comprises two opto-couplers (SD1, SD2) connected in anti-parallel and a resistor (R) connected in parallel with said opto-couplers, and an evaluation circuit (AS) connected to the detector (SDS), such method being characterized in that:
- the durations of positive and negative half-waves of the loop current (I) are measured during an evaluation period, when the sum of the two durations is less than a first fixed presettable threshold the evaluation circuit (AS) detects occurrence of an interruption or a short-circuit to earth in the other of the subscriber wires, when there is a ratio of approximately 1:1 (second presettable threshold) between the two durations the evaluation circuit (AS) detects the ringing alternating current transmitted while the subscriber line loop is open, and at a ratio of approximately 1:1.5 (third presettable threshold) between the two durations the evaluation circuit (AS) detects the transmission of ringing alternating current while the subscriber line loop is closed, and when the ratio between the two durations substantially exceeds 1:1.5 the evaluation circuit (AS) detects a short-circuit to earth in said one subscriber wire.
Dependencies are inferred from the claim text.