Circuit arrangement for determining the connection condition of a subscriber line in a telecommunications network

Claim 1

A circuit arrangement for determining the connections conditions of a plurality of subscriber lines in a telecommunications network, each of said subscriber lines having two wires extending between a subscriber station and a subscriber line interface circuit, said two wires being connected in said subscriber line interface circuit via respective resistors to the two poles of a DC voltage source, said circuit arrangement comprising in combination: (a) first comparator means (K1) having first and second inputs and an output, said first comparator means producing a first output signal at its output indicating the presence of a first group of operating conditions; (b) second comparator means (K2) having first and second inputs and an output, said second comparator means producing a second output signal at its output indicating the presence of a second group of operating conditions; (c) a first sampling point (Sb) in each subscriber line interface circuit presenting a first voltage condition thereof; (d) a second sampling point (Sm) in each subscriber line interface circuit presenting a second voltage condition thereof; (e) first selector means (M1) having parallel signal inputs, an output and a control input for receiving an address control signal for selectively connecting each one of said signal inputs to said output during a monitoring cycle, each of said signal inputs of said first selector means being coupled to a first sampling point of one of said subscriber line interface circuits; (f) second selector means (M2) having parallel signal inputs, an output and a control input for receiving an address control signal for selectively connecting each one of said signal inputs to said signal output during a monitoring cycle, each of said signal inputs being coupled to a second sampling point of one of said subscriber line interface circuits, at least one input of each of said first and second comparator means being coupled to said first and said second sampling points via said first and second selector means and a respective voltage divider; (g) central control means (ZST and S) for selecting certain operating conditions of each subscriber line interface circuit; (h) first reference voltage source means, responsive to said central control means, for producing a first reference voltage in accordance with the selected operating condition of the monitored subscriber line interface circuit, said first reference voltage being coupled to one of said inputs of said first comparator means; (i) a plurality of filter capacitors (Cl to Cn); (j) means coupling a separate one of said capacitors across said inputs of said first comparator means for every selection position of said first and second selector means; and (k) signal enabling means, coupled to the outputs of said first and second comparator means, for passing said second output signal in dependence upon the state of said first output signal and the selected operating condition of the monitored subscriber line interface circuit.