| 摘要 |
The present invention relates to the detection of inoperable and line busy conditions on telephone lines. It relates to the detection of open-circuits or short circuits between the telephone exchange and the telephone receiver or at the receiver and to alerting the subscriber to take corrective action. It also relates to the detection of line busy conditions for individual users across one common line so that any user can identify that the line is being used. Apparatus for connection to the telephone line includes detection means (3) to detect the presence of a low voltage on the telephone line; alarm means (12) to alert the user in response to detection of such a low voltage; and a line busy voltage detection means to detect the line busy signal and indicate the user that the line is being engaged. |
