Electronic remote supervision and control of states and processes

Claim 1

A remote-condition monitoring and control apparatus for use at a subscriber station in conjunction with a preexisting telephone system, said apparatus comprising a Graetz bridge circuit having a pair of input terminals adaptable for connection to a pair of telephone lines from said preexisting telephone system and a pair of output terminals, voltage detecting means connected to said Graetz bridge output terminals for detecting the presence of incoming a.c. call signals from a remote supervisor station on said pair of telephone lines, summing means for counting the number of said incoming call signals connected to the output of said voltage detecting means, condition monitoring means operative to detect a predetermined physical parameter, switching means connected to the output of said summing means and operative in response thereto when the number of said incoming calls exceeds a predetermined number to selectively connect said condition monitoring means to said preexisting telephone lines to simulate answering of a telephone at said subscriber station and to maintain connection with said telephone lines for a predetermined time period, audio frequency detecting means connected to the output of said switching means and operative in response thereto after said simulated answering at said subscriber station to discriminate between audio command signals over said telephone lines by detecting the frequency of said audio command signals emanating from said remote supervisor station, and control signal generator means connected to the output of said audio frequency detecting means operative in response to said detected supervisory audio command signal to produce a supervisory control signal.