Subscriber pressure alarm system

Claim 2

A monitoring circuit for detecting the occurrence of a predetermined condition comprising: a. a pair of electrical conductors bridged by a current leakage path made up of resistance means and normally closed switch means connected in series with said resistance means, said switch means being adapted to be opened upon the occurrence of said predetermined condition; and, b. an alarm activating circuit including: a resistor electrically in series with one of said conductors and connected to a control circuit bridging said pair of electrical conductors, said control circuit being rendered electrically nonconductive in response to a predetermined voltage drop occurring across said resistor and caused by current flow through said current leakage path and said resistor when said switch means is closed, and said control circuit being rendered electrically conductive in response to a decrease of said voltage drop.

Claim 3

A monitoring circuit as defined in claim 1, wherein an additional resistance is arranged to disconnectably bridge said pair of electrical conductors, said additional resistance being of a value lower than that of said resistance means so that when said additional resistance is connected in bridging relation across said conductors, said current leakage path is shunted.

Claim 4

A monitoring circuit as defined in claim 2, wherein said additional resistance forms a part of a telephone set.

Claim 5

A monitoring circuit as defined in claim 1, wherein a resistive test means is selectively connectable between said pair of electrical conductors and is adapted for electrically connecting a resistor, equivalent in value to said leakage path, between said electrical conductors.

Claim 6

A monitoring circuit as defined in claim 1, wherein testing means is provided for shunting said resistor.

Claim 7

A monitoring circuit as defined in claim 1, wherein said control circuit includes means for operating an alarm in response to the electrically conductive state of said control circuit.

Claim 8

A monitoring circuit as defined in claim 1, wherein said control circuit includes transistors means, circuit connection means for rendering said transistor means electrically nonconductive in response to said voltage drop decrease, and means controlled by said transistor means for operating an alarm to indicate the occurrence of said condition.

Claim 9

A monitoring circuit as defined in claim 1, wherein said control circuit contains a first transistor connected to one of said electrical conductors, said first transistor being also connected through a voltage dividing network to a second transistor, which in turn is connected to the remaining electrical conductor and a means for activating an alarm, which in turn is connected to the first-mentioned conductor, said second transistor having an electrically conductive state and an electrically nonconductive state, said first transistor being responsive to said decrease in said voltage drop to place said second transistor in a predetermined one of said states, and said alarm activating means being conditioned by said second transistor when in said predetermined one of said states to operate said alarm.

Claim 10

A monitoring circuit as defined in claim 1, wherein said control circuit is in electrical connection with the other of said electrical conductors through a diode.

Claim 11

A monitoring circuit as defined in claim 3, wherein said electrical conductors are connected to a power supply means in a telephone central office, said power supply means providing a source for said current flow through said leakage path and said resistor.

Claim 12

A monitoring circuit As defined in claim 1, wherein said current leakage path is enclosed by cable sheath.

Claim 13

A monitoring circuit as defined in claim 1, wherein said switch means are pressure responsive.

Claim 14

A monitoring circuit comprising: a. a current leakage path having first and second terminals adapted to be connected to a pair of conductors of a multiple conductor transmission line, said leakage path being defined by resistance means and normally closed switch means connected in series with said resistance means between said terminals, said switch means being adapted to be opened upon the occurrence of a predetermined monitored condition; and b. an alarm activating circuit including a resistor connected in series with one of said conductors and a control circuit bridged across said conductors, said resistor being connected to said first terminal, and said control circuit being connected to said resistor and to said second terminal, said control circuit being rendered electrically nonconductive in response to a predetermined voltage drop occurring across said resistor and caused by current flowing through said current leakage path and through said resistor when said switch means is closed, and said control circuit being rendered electrically conductive in response to a decrease of said voltage drop.

Claim 15

A monitoring circuit comprising: a. a current leakage path having first and second terminals adapted to be connected to a pair of conductors of a multiple conductor transmission line, said leakage path being defined by resistance means and normally closed switch means connected in series with said resistance means between said terminals, said switch means being adapted to be opened upon the occurrence of a predetermined monitored condition; and b. an alarm activating circuit including a resistor connected in series with one of said conductors and a control circuit bridged across said conductors, said resistor being connected to said first terminal, and said control circuit being connected to said resistor and to said second terminal, said control circuit being rendered electrically nonconductive in response to a predetermined voltage drop occurring across said resistor and caused by current flowing through said current leakage path and through said resistor when said switch means is closed, and said control circuit being rendered electrically conductive in response to a decrease of said voltage drop.

Claim 16

A monitoring circuit as defined in claim 13, wherein a resistive test means has a further resistor, equivalent in value to said leakage path and means for selectively and disconnectably bridging said further conductor across said conductors.

Claim 17

A monitoring circuit as defined in claim 13, wherein testing means is provided for shunting said resistor.

Claim 18

A monitoring circuit as defined in claim 13, wherein said control circuit contains a means for operating an alarm in response to the electrically conductive state of said control circuit.

Claim 19

A monitoring circuit as defined in claim 13, wherein said control circuit contains transistor means and circuit connection means for rendering said transistor means electrically nonconductive by said predetermined voltage drop when said switch means is closed and for rendering said transistor means electrically conductive in response to said decrease of said voltage drop, and means conditioned by said transistor means for operating an alarm when said transistor means is in its conductive state.

Claim 20

A monitoring circuit as defined in claim 13, wherein said control circuit contains a first transistor connected to said resistor and also through a voltage dividing network to a second transistor which in turn is connected (i) to said current leakage path and (ii) to a means for activating an alarm that is also connected to said resistor, said first and second transistors having electrically conductive and electrically nonconductive states, said first transistor being placed in a predetermined one of said states in response to said decrease in said voltage drop, and said second transistor being operated to one of its predetermined states when said first transistor is operated to its predetermined one of said states to condition said alarm activating means for activating said alarm.

Claim 21

A monitoring circuit as defined in claim 13, wherein said control circuit is connected through a diode to said current leakage path.

Claim 22

A monitoring circuit as defined in claim 13, wherein said switch means are pressure responsive.

Claim 23

A monitoring system comprising circuit means having a two conductor transmission line, first resistance means connected in series with one of the conductors of said transmission line, an electrical power source connected across the conductors of said transmission line to provide for a flow of current through said first resistance means when a circuit is completed between said conductors of said transmission line, a device for detecting the occurrence of a predetermined condition and having normally closed contact means, a current leakage network containing said contact means and second resistance Means in series with said contact means, said current leakage network being bridged across said conductors for completing a circuit across said conductors to enable current to flow serially through said second resistance means and said contact means when said contact means are closed, said contact means being adapted to open in response to the occurrence of said predetermined condition to provide for a predetermined variation in said flow of current through said first resistance means for varying the voltage measured across said first resistance means, and means connected to said conductors and being responsive to the voltage measured across said resistance means for signalling the presence of said predetermined condition when said predetermined variation occurs.

Claim 24

A monitoring system comprising circuit means having a two conductor transmission line, first resistance means connected in series with one of the conductors of said transmission line, an electrical power source connected across the conductors of said transmission line to provide for a flow of current through said first resistance means when a circuit is completed between said conductors of said transmission line, a device for detecting the occurrence of a predetermined condition and having normally closed contact means, a current leakage network containing said contact means and second resistance Means in series with said contact means, said current leakage network being bridged across said conductors for completing a circuit across said conductors to enable current to flow serially through said second resistance means and said contact means when said contact means are closed, said contact means being adapted to open in response to the occurrence of said predetermined condition to provide for a predetermined variation in said flow of current through said first resistance means for varying the voltage measured across said first resistance means, and means connected to said conductors and being responsive to the voltage measured across said resistance means for signalling the presence of said predetermined condition when said predetermined variation occurs.

Claim 25

The monitoring system defined in claim 21 wherein said means for signalling the presence of said predetermined condition when said predetermined variation occurs comprises a transistorized circuit electrically connected across said conductors in parallel relation to said contact means.

Claim 26

The monitoring system defined in claim 21 wherein said device is pressure responsive and wherein said predetermined condition is a predetermined change in pressure.

Claim 27

In a telephone system having a telephone set and circuit means including a two conductor transmission line for connecting said set to a central office terminal, electrical resistance means connected in series with one of the conductors of said transmission line to provide for a voltage drop across said resistance means when a circuit is completed between the conductors of said transmission line, a condition detecting device having normally closed switch means, a circuit branch containing said switch means and a resistor in series with said switch means, said circuit branch being bridged across said conductors in parallel relation with said telephone set for completing a circuit across said conductors in absence of a predetermined condition, said switch means being adapted to open in response to the occurrence of said predetermined condition to provide for a predetermined variation in the voltage measured across said resistance means, and means responsive to the voltage measured across said resistance means for signalling the occurrence of said predetermined condition when said predetermined variation occurs.

Claim 28

In a telephone system having a telephone set and circuit means including a two conductor transmission line for connecting said set to a central office terminal, electrical resistance means connected in series with one of the conductors of said transmission line to provide for a voltage drop across said resistance means when a circuit is completed between the conductors of said transmission line, a condition detecting device having normally closed switch means, a circuit branch containing said switch means and a resistor in series with said switch means, said circuit branch being bridged across said conductors in parallel relation with said telephone set for completing a circuit across said conductors in absence of a predetermined condition, said switch means being adapted to open in response to the occurrence of said predetermined condition to provide for a predetermined variation in the voltage measured across said resistance means, and means responsive to the voltage measured across said resistance means for signalling the occurrence of said predetermined condition when said predetermined variation occurs.

Claim 29

The telephone system defined in claim 24, wherein said predetermined condition constitute a predetermined variation in pressure in a pressurized cable that forms a part of said transmission line, and wherein said switch means is opened in response to said predetermined variation of pressure.

Claim 30

In a telephone system having a telephone set transferrable between on-hook and off-hook states and circuit means including a two conductor transmission line for connecting said set to a central office terminal, said telephone set being operative to complete a first circuit between the conductors of said transmission line when transferred to said off-hook state and to interrupt said first circuit when transferred to said on-hook state, detecting means for monitoring a predetermined condition, said detecting means having normally closed switch means, a circuit branch containing said switch means and first resistance means in series with said switch means, said circuit branch providing a second circuit bridged across said conductors in the absence of said predetermined condition, said switch means being adapted to open upon the occurrence of said predetermined condition to interrupt said second circuit, second resistance means connected in one of the conductors of said transmission line in series with said first and second circuits, a power source connected across the conductors of said transmission line to provide for a flow of current through and a voltage drop across said second resistance means whenever either or both of said first and second circuits are completed, said first and second circuits, upon being concomitantly interrupted, providing for a prEdetermined variation in the voltage measured across said second resistance means, and voltage responsive circuit means electrically connected to said transmission line and being responsive to the occurrence of said predetermined variation to provide a signal indicating the occurrence of said predetermined condition.

Claim 31

In a telephone system having a telephone set transferrable between on-hook and off-hook states and circuit means including a two conductor transmission line for connecting said set to a central office terminal, said telephone set being operative to complete a first circuit between the conductors of said transmission line when transferred to said off-hook state and to interrupt said first circuit when transferred to said on-hook state, detecting means for monitoring a predetermined condition, said detecting means having normally closed switch means, a circuit branch containing said switch means and first resistance means in series with said switch means, said circuit branch providing a second circuit bridged across said conductors in the absence of said predetermined condition, said switch means being adapted to open upon the occurrence of said predetermined condition to interrupt said second circuit, second resistance means connected in one of the conductors of said transmission line in series with said first and second circuits, a power source connected across the conductors of said transmission line to provide for a flow of current through and a voltage drop across said second resistance means whenever either or both of said first and second circuits are completed, said first and second circuits, upon being concomitantly interrupted, providing for a prEdetermined variation in the voltage measured across said second resistance means, and voltage responsive circuit means electrically connected to said transmission line and being responsive to the occurrence of said predetermined variation to provide a signal indicating the occurrence of said predetermined condition.

Claim 32

The telephone system defined in claim 26 wherein the completion of said first circuit provides a voltage drop across said second resistance means that prevents said voltage responsive circuit means from being conditioned to signal the occurrence of said predetermined condition even when said second circuit is interrupted.

Claim 33

The telephone system defined in claim 27 wherein said circuit means is bridged across said conductors to receive operating power from said power source.