| 摘要 |
The invention relates to a circuit arrangement for centrally controlled telephone switching systems, in particular telephone PBX systems, with subscriber terminals which are equipped with earth keys to forward call connections or to set up line connections to the operator's position, and whose a/b wires are monitored for loop current changes, short-circuits and earth faults. The indication device (IE) has the first switching means (S) for loop current monitoring of the a/b wires within a specific current range, while the second switching means (SU) is activated when the upper limit of the loop current is exceeded, and the third switching means (X) signals the >>earth fault<< when the current level falls below a specific value on the b wire. This circuit arrangement can be used for line-individual loop current change monitoring in centrally controlled telephone switching systems for analog and digital subscriber terminals. <IMAGE>
|
