Telephone instrument disconnect circuit

Claim 2

In a remote disconnect circuit for enabling the disconnection of subscriber''s telephone instrument from a pair of line conductors by which telephone service is normally extended from a Central Office, the telephone instrument including a receiver, a pair of line terminals for connection to the pair of line conductors and means for selectively coupling the receiver to the pair of line terminals to provide a closed d.c. circuit across the line terminals, the disconnect circuit comprising: switch means connected in at least one of said pair of line conductors between the Central Office and the telephone instrument line terminals for selectively disconnecting or connecting at least one of the line terminals from the respective line conductor; and first control means connected to the line conductors and responsive to a closed d.c. circuit across the line terminals and to the application of a control signal on the line conductors for operating said switch means to disconnect the telephone instrument line terminals from the line conductors only when the telephone instrument''s receiver is connected across the line terminals.

Claim 3

The disconnect circuit as defined in claim 1 including second control means connected to the line terminals and responsive to the opening of the d.c. circuit across line terminals for operating the switch means to reconnect said at least one of the line conductors to the respective line terminals.

Claim 4

The disconnect circuit as defined in claim 1 wherein the first control means includes a control signal detector having an input and an output and arranged to provide an output signal in the output thereof in response to the application of the control signal to the input thereof, means coupled between the switch means and the output of the control signal detector for operating the switch means in response to the output signal and means for coupling the input circuit of the control signal detector to the line conductors.

Claim 5

The disconnect circuit as defined in claim 3 wherein the first control means further includes means for detecting loop current in the line conductors when the conductors are interconnected to thereby sense the presence of a closed circuit across the line terminals and for coupling the input circuit of the control signal detector to the line conductors when loop current is detected.

Claim 6

The disconnect circuit as defined in claim 3 wherein the switch means includes a first latching relay with contacts connected in series with at least oNe of the line conductors for disconnecting and connecting the line conductors to the instrument terminates when the contacts are open and closed respectively.

Claim 7

The disconnect circuit as defined in claim 5 wherein the means for detecting loop current in the line conductors includes a second latching relay having at least one coil connected in series with the line conductors.

Claim 8

The disconnect circuit as defined in claim 4 wherein the control signal detector includes at least one bandpass filter, the bandpass filter being arranged to provide an output signal in response to the control signal having a frequency within the bandpass characteristics of said filter.

Claim 9

The disconnect circuit as defined in claim 7 wherein said filter includes integrating means for providing an output signal only in response to a control signal having a frequency with the bandpass characteristics of the filter for a predetermined period of time.

Claim 10

The disconnect circuit as defined in claim 7 wherein the control signal detector includes a pair of bandpass filters and integrators, the filters and integrators having different bandpass characteristics and arranged to provide an output signal only in response to a control signal having a frequency within each bandpass characteristic for a predetermined period of time.

Claim 11

The disconnect circuit as defined in claim 4 including a bridge rectifier network connected across the line for providing bias voltages for the first and second control means.

Claim 12

In a telephone system for permitting an operator at a Central Office to disconnect a telephone instrument which has seized a party line from the pair of line conductors through which service is extended to a plurality of instruments by applying a control signal to the line conductors at the Central Office, the Central Office having a source of direct current which is connected to the pair of line conductors to cause current to flow through the conductors and the instrument when the line conductors are seized by a telephone instrument, each telephone instrument including a receiver, a pair of line terminals for connection to the line conductors and a switch for selectively coupling the receiver to the line terminals to thereby seize the party line, a remote disconnect circuit connected individually between the Central Office and each telephone instrument, each circuit comprising: switch means connected in at least one of said pair of line conductors between the Central Office and the telephone instrument line terminals for selectively disconnecting or connecting at least one of the line terminals to the respective line conductor; first control means connected to the line conductors and responsive to the seizure of the line conductors by the instrument''s receiver and to the presence of a control signal on the line conductors for operating the switch means to disconnect at least one of the instrument''s line terminals from the respective line conductor; and second control means connected to the line terminals and responsive to the interruption of line current caused by the disconnection of the receiver from the line terminals for operating the switch means to reconnect said at least one of the line conductors to the respective line terminal so that each terminal is connected to its respective line conductor.

Claim 13

In a telephone system for permitting an operator at a Central Office to disconnect a telephone instrument which has seized a party line from the pair of line conductors through which service is extended to a plurality of instruments by applying a control signal to the line conductors at the Central Office, the Central Office having a source of direct current which is connected to the pair of line conductors to cause current to flow through the conductors and the instrument when the line conductors are seized by a telephone instrument, each telephone instrument including a receiver, a pair of line terminals for connection to the line conductors and a switch for selectively coupling the receiver to the line terminals to thereby seize the party line, a remote disconnect circuit connected individually between the Central Office and each telephone instrument, each circuit comprising: switch means connected in at least one of said pair of line conductors between the Central Office and the telephone instrument line terminals for selectively disconnecting or connecting at least one of the line terminals to the respective line conductor; first control means connected to the line conductors and responsive to the seizure of the line conductors by the instrument''s receiver and to the presence of a control signal on the line conductors for operating the switch means to disconnect at least one of the instrument''s line terminals from the respective line conductor; and second control means connected to the line terminals and responsive to the interruption of line current caused by the disconnection of the receiver from the line terminals for operating the switch means to reconnect said at least one of the line conductors to the respective line terminal so that each terminal is connected to its respective line conductor.

Claim 14

The disconnect circuit as defined in claim 11 wherein the switch means includes a first latching relay with contacts connected in series with at least one of the line conductors so that consecutive operation of the first relay disconnects and then connects said at least one of the line conductors to the respective instrument''s line terminal.

Claim 15

The disconnect circuit as defined in claim 12 wherein the first control means includes a second latching relay connected in series with the line conductors, the seocnd relay being arranged to be operated by d.c. current flow through the line conductors when the line conductors are seized by the insTrument''s receiver.

Claim 16

The disconnect circuit as defined in claim 13 wherein the second control means includes means coupled to the line conductors between the Central Office and the switch means for operating the first latching relay when the switch means has disconnected said at least one of the line terminals from the respective line conductor and when the instrument''s receiver is disconnected from the line terminals.