Open circuit and ground detector for fire and burglar alarm system

Claim 2

The combination of first and second transistors each having a base and an emitter and a collector, a source of bias currents, third and fourth transistors each having a base and an emitter and a collector, a first conductive path between the base and emitter of the first transistor, a second conductive path between the base and emitter of the second transistor, the collector-emitter circuits of the four transistors being connected in parallel, and means, including a first resistor between ground and the emitters of the first and third transistors and a second resistor between ground and the emitters of the second and fourth transistors, for biasing the four transistors so that, in response to an open on either of said conductive paths one of the first and second transistors becomes conductive and so that in response to a ground on either of said paths one of said resistors is short-circuited and one of the third and fourth transistors becomes conductive, a trouble-indicating network coupled to the collectors of all of said transistors and responsive to collector current in any of the first, second, third or fourth transistors to indicate a fault in one of said conductive paths, normally open switch contacts between said conductive paths, fifth and sixth transistors each having a base and an emitter and a collector, the emitters of the fifth and sixth transistors being connected to the bases of the first and second transistors, respectively, the bases of the fifth and sixth transistors being coupled to the emitters of the second and first transistors, respectively, and the collectors of the fifth and sixth transistors being connected in parallel, an alarm indicator in series with the collectors of said fifth and sixth transistors and responsive to the absence of collector currents in both of the fifth and sixth transistors to provide an alarm, and means for completing the biasing on said fifth and sixth transistors so that the sixth transistor conducts in the absence of any open or ground in either path.

Claim 3

The combination of first and second transistors each having a base and an emitter and a collector, a source of bias currents, first and second conductive paths between the respective bases and emitters of the first and second transistors, third and fourth transistors each having a base and an emitter and a collector, the collector-emitter circuits of said four transistors being connected in parallel, and means, including a first resistor between gRound and the emitters of the first and third transistors and a second resistor between ground and the emitters of the second and fourth transistors, for biasing said four transistors so that, in response to an open circuit on any of said conductive paths one of the first and second transistors becomes conductive and so that in response to a ground on any one of said paths one of said resistors is short-circuited and one of the third and fourth transistors becomes conductive.

Claim 4

The combination of first and second transistors each having a base and an emitter and a collector, a source of bias currents, first and second conductive paths between the respective bases and emitters of the first and second transistors, third and fourth transistors each having a base and an emitter and a collector, the collector-emitter circuits of said four transistors being connected in parallel, and means, including a first resistor between gRound and the emitters of the first and third transistors and a second resistor between ground and the emitters of the second and fourth transistors, for biasing said four transistors so that, in response to an open circuit on any of said conductive paths one of the first and second transistors becomes conductive and so that in response to a ground on any one of said paths one of said resistors is short-circuited and one of the third and fourth transistors becomes conductive.

Claim 5

The combination in accordance with claim 2, and a trouble-indicating network coupled to the collectors of all of said transistors and responsive to collector current in any of them to indicate a fault in one of said conductive paths.

Claim 6

The combination in accordance with claim 3, normally open contacts between said conductive paths, fifth and sixth transistors each having a base and an emitter and a collector, the emitters being connected to the bases of the first and second transistors, respectively, the bases of the fifth and sixth transistor being coupled to the emitters of the second and first transistors, respectively, and the collectors of the fifth and sixth transistors being connected in parallel, an alarm indicator in series with the collectors of said fifth and sixth transistors and responsive to the absence of collector currents in both of the fifth and sixth transistors to provide an alarm, and means for completing the biasing of said fifth and sixth transistors so that the sixth transistor conducts in the absence of any open or ground in either path.

Claim 7

In a burglar and fire alarm system of the type which includes a sensor having a normally open pair of contacts, a first pair of transmission lines connected to one of said contacts and a second pair of transmission lines connected to the other one of said contacts, the combination of: a first transistor having an emitter and a base and a collector, a second transistor having an emitter and a base and a collector, the first and second lines being connected in series between the emitter and base of the first transistor and the third and fourth lines being connected in series between the emitter and base of the second transistor, a trouble-indicating network which responds to collector flow in either the first or second transistor, the collectors of the first and second transistors being in series with said network, means for biasing said first and second transistors so that an open on any of the lines causes the emitter of one of the first and second transistors to become biased in a conductive direction and to apply collector current to said trouble-indicating network, third and fourth transistors each having a collector and a base and an emitter, the collectors of the third and fourth transistors being in series with said trouble-indicating network, means for so biasing the third and fourth transistors that if a ground develops in any of said lines, collector current of one of the third and fourth transistors flows into said trouble-indicating network, an alarm indicating network, fifth and sixth transistors each having a base and an emitter and a collector, the emitters of the fifth and sixth transistors being respectively coupled to the bases of the first and second transistors, and the bases of the fifth and sixth transistors being coupled to the emitters of the second and first transistors, and means for completing the biasing of said fifth and sixth transistors so that both are nonconductive when said contacts are closed and so that the sixth transistor is conductive when said contacts are open and in the absence of any ground or open circuit on said lines, the alarm-indicating network being in series with the collectors of the fifth and sixth transistors and responding to a nonconducting condition of both the fifth and sixth transistors to send out an alarm.

Claim 8

In a burglar and fire alarm system of the type which includes a sensor having a normally open pair of contacts, a first pair of transmission lines connected to one of said contacts and a second pair of transmission lines connected to the other one of said contacts, the combination of: a first transistor having an emitter and a base and a collector, a second transistor having an emitter and a base and a collector, the first and second lines being connected in series between the emitter and base of the first transistor and the third and fourth lines being connected in series between the emitter and base of the second transistor, a trouble-indicating network which responds to collector flow in either the first or second transistor, the collectors of the first and second transistors being in series with said network, means for biasing said first and second transistors so that an open on any of the lines causes the emitter of one of the first and second transistors to become biased in a conductive direction and to apply collector current to said trouble-indicating network, third and fourth transistors each having a collector and a base and an emitter, the collectors of the third and fourth transistors being in series with said trouble-indicating network, means for so biasing the third and fourth transistors that if a ground develops in any of said lines, collector current of one of the third and fourth transistors flows into said trouble-indicating network, an alarm indicating network, fifth and sixth transistors each having a base and an emitter and a collector, the emitters of the fifth and sixth transistors being respectively coupled to the bases of the first and second transistors, and the bases of the fifth and sixth transistors being coupled to the emitters of the second and first transistors, and means for completing the biasing of said fifth and sixth transistors so that both are nonconductive when said contacts are closed and so that the sixth transistor is conductive when said contacts are open and in the absence of any ground or open circuit on said lines, the alarm-indicating network being in series with the collectors of the fifth and sixth transistors and responding to a nonconducting condition of both the fifth and sixth transistors to send out an alarm.