Combined audio program and alarm signaling system with line supervision

Claim 1

A LINE FAULT SUPERVISION ARRANGEMENT IN A SIGNALING SYSTEM COMPRISING: A TWO-WIRE TELEPHONE LINE; A FIRST DIRECT CURRENT SOURCE AT ONE END OF THE LINE FOR APPLYING A FIRST D.C SUPERVISORY CURRENT TO ONE WIRE OF THE LINE; FIRST RESISTANCE MEANS AT THE OPPOSITE END OF SAID LINE TERMINATING SAID ONE WIRE TO GROUND FOR D.C.; A SECOND DIRECT CURRENT SOURCE AT SAID ONE END OF THE LINE FOR APPLYING A SECOND D.C. SUPERVISORY CURRENT TO THE OTHER WIRE OF SAID LINE; SECOND RESISTANCE MEANS AT THE OPPOSITE END OF SAID LINE TERMINATING SAID OTHER WIRE TO GROUND FOR D.C.; AND MEANS AT SAID ONE END OF THE LINE OPERABLE IN RESPONSE TO AN ABNORMAL SUPERVISORY CURRENT IN EITHER WIRE TO INDICATE A FAULT ON THE LINE.