Fibre optic security system

Claim 2

In a security alarm system comprising at least one sensor unit, a control unit, a connection between the sensor unit and the control unit, and an alarm circuit conditionable by said control unit to an alarm condition, the sensor unit being operative to apply a signal to the connection and to switch that signal from a normal state in response to sensing an abnormal condition, and the control unit being operative to monitor said signal for deviation from its normal state and to condition said alarm circuit in response to detection of such a deviation, the improvement in which the sensor unit includes an optoelectronic transmitter and the control unit includes first and second optoelectronic receivers, the said connection is established by a flexible optical light fibre guide coupled to said optoelectronic transmitter in the sensor unit and said first optoelectronic receiver in the control unit for transmission of said signal in the form of light from the sensor unit for reception by the control unit, and the control unit monitors at least one parameter of the signal in its normal state which is dependent upon the optical integrity of the guide for deviation outside predetermined limits, the optical fibres of said guide form two sub-bundles the fibres of which are intermingled intermediate the ends of the guide, one of the two sub-bundles being optically coupled to said transmitter and said first receiver and the other of the two sub-bundles being optically coupled to said second optoelectronic receiver but isolated from said transmitter.

Claim 3

In a security alarm system in which a sensor unit for sensing an alarm condition is linked by a signalling path to alarm control means at a second location, said sensor unit including means operative to apply a normal signal condition to said path at said first location for transmission via said path for reception by said alarm control means, and switch means responsive to the sensing of the alarm condition to effect change in the said applied signal condition, and in which the alarm control means includes a condition responsive alarm circuit, and signal-receiving means coupled to said signalling path at said second location to condition said alarm circuit for response upon sensing change from said normal signal condition as received from said path by said alarm control means, the improvement wherein said signalling path is a fibre-optic light guide extending between said first and second locations, the means included by said sensor unit for applying a signal condition to said path comprise light-emitting means at said first location continuously coupled to said guide for transmitting a light signal within said guide from said first location towards said second location, and said signal-receiving means includes means for responding to change in the light signal received from said guide at said second location to condition said alarm circuit for response, and wherein the light guide comprises a plurality of optical fibres, the said sensor unit transmits the said light signal into only some of the said optical fibres of the light guide, and said alarm control means includes means to condition said alarm circuit for response upon reception of said light signal from the others of said optical fibres.

Claim 4

In a security alarm system in which a sensor unit for sensing an alarm condition is linked by a signalling path to alarm control means at a second location, said sensor unit including means operative to apply a normal signal condition to said path at said first location for transmission via said path for reception by said alarm control means, and switch means responsive to the sensing of the alarm condition to effect change in the said applied signal condition, and in which the alarm control means includes a condition responsive alarm circuit, and signal-receiving means coupled to said signalling path at said second location to condition said alarm circuit for response upon sensing change from said normal signal condition as received from said path by said alarm control means, the improvement wherein said signalling path is a fibre-optic light guide extending between said first and second locations, the means included by said sensor unit for applying a signal condition to said path comprise light-emitting means at said first location continuously coupled to said guide for transmitting a light signal within said guide from said first location towards said second location, and said signal-receiving means includes means for responding to change in the light signal received from said guide at said second location to condition said alarm circuit for response, and wherein the light guide comprises a plurality of optical fibres, the said sensor unit transmits the said light signal into only some of the said optical fibres of the light guide, and said alarm control means includes means to condition said alarm circuit for response upon reception of said light signal from the others of said optical fibres.

Claim 5

In a security alarm system in which a sensor unit for sensing an alarm condition is linked by a signalling path to alarm control means at a second location, said sensor unit including means operative to apply a normal signal condition to said path at said first location for transmission via said path for reception by said alarm control means, and switch means responsive to the sensing of the alarm condition to effect change in the said applied signal condition, and in which the alarm control means includes a condition respective alarm circuit, and signal-receiving means coupled to said signalling path at said second location to condition said alarm circuit for response upon sensing change from said normal signal condition as received from said path by said alarm control means, the improvement wherein said signalling path is a fibre-optic light guide extending between said first and second locations, the means included by said sensor unit for applying a signal condition to said path comprise light-emitting means at said first location continuously coupled to said guide for transmitting a light signal within said guide from said first location towards said second location, and said signal-receiving means includes means for responding to change in the light signal received from said guide at said second location to condition said alarm circuit for response, and wherein the light guide comprises two sub-bundles of optical fibres that are intermingled with one another between the said sensor unit and the said alarm control means, and wherein the sensor unit transmits the said light signal into only a first of the two sub-bundles and the alarm control means includes sensing means associated with said second sub-bundle to condition said alarm circuit for response upon sensing light output from said second sub-bundle.

Claim 6

In a security alarm system in which a sensor unit for sensing an alarm condition is linked by a signalling path to alarm control means at a second location, said sensor unit including means operative to apply a normal signal condition to said path at said first location for transmission via said path for reception by said alarm control means, and switch means responsive to the sensing of the alarm condition to effect change in the said applied signal condition, and in which the alarm control means includes a condition respective alarm circuit, and signal-receiving means coupled to said signalling path at said second location to condition said alarm circuit for response upon sensing change from said normal signal condition as received from said path by said alarm control means, the improvement wherein said signalling path is a fibre-optic light guide extending between said first and second locations, the means included by said sensor unit for applying a signal condition to said path comprise light-emitting means at said first location continuously coupled to said guide for transmitting a light signal within said guide from said first location towards said second location, and said signal-receiving means includes means for responding to change in the light signal received from said guide at said second location to condition said alarm circuit for response, and wherein the light guide comprises two sub-bundles of optical fibres that are intermingled with one another between the said sensor unit and the said alarm control means, and wherein the sensor unit transmits the said light signal into only a first of the two sub-bundles and the alarm control means includes sensing means associated with said second sub-bundle to condition said alarm circuit for response upon sensing light output from said second sub-bundle.

Claim 7

A security alarm system according to claim 3, wherein the alarm control means includes first and second light-responsive devices for responding electrically to light output of the first and second sub-bundles respectively, a signal-deriving circuit coupled to said first light-responsive device to derive an electrical signal having a magnitude dependent on at least one parameter of light received by said first light-responsive device from said first sub-bundle, an electrical monitoring circuit for monitoring the magnitude of this derived signal to condition said alarm circuit for response upon departure of the signal magnitude from a predetermined range, the said second light-responsive device being coupled to the said signal-deriving circuit to cause the derived signal-magnitude to depart from said range in response to reception by said second light-responsive device of light from the said second sub-bundle.