Alarm system with periodic test section

Claim 2

An alarm system, comprising: detecting means for producing a change in an electrical parameter from a normal non-alarm value in response to the occurrence of an alarm state; an alarm state detecting circuit including trigger means connected to said detecting means for providing an output when said electrical parameter has a value beyond a predetermined threshold value; an alarm signalling circuit for producing an alarm signal in response to the output of said trigger means; test means for automatically changing said predetermined threshold value to a value beyond said normal electrical parameter value.

Claim 3

A system according to claim 1 in which said detecting means comprises a sensing device having at least two different impedance states, a first being a normal non-alarm state incapable of actuating said trigger means except upon said change of threshold value by said test means, and a second corresponding to a preselected alarm state and hence to an electrical parameter value beyond said predetermined threshold value of said trigger means.

Claim 4

An alarm system comprising in combination: detecting means including electrical conductors having an impedance therebetween of value at least partly dependent on the alarm state to be detected; an electrical alarm signalling device connected to said electrical conductors and including an alarm state detecting portion and an alarm signalling portion, said alarm state detecting portion comprising a trigger amplifier having an input in current circuit with said electrical conductors; and test means connected to said alarm state detecting portion for automatically at intervals changing the trigger level of said trigger amplifier such that the trigger amplifier operates in response to the normal non-alarm impedance between said conductors, said trigger amplifier in the periods between said intervals having a different trigger level, said different tRigger level being that wherein said normal non-alarm impedance places said trigger amplifier in an alarm preparatory state but does not operate said trigger amplifier.

Claim 5

An alarm system comprising in combination: detecting means including electrical conductors having an impedance therebetween of value at least partly dependent on the alarm state to be detected; an electrical alarm signalling device connected to said electrical conductors and including an alarm state detecting portion and an alarm signalling portion, said alarm state detecting portion comprising a trigger amplifier having an input in current circuit with said electrical conductors; and test means connected to said alarm state detecting portion for automatically at intervals changing the trigger level of said trigger amplifier such that the trigger amplifier operates in response to the normal non-alarm impedance between said conductors, said trigger amplifier in the periods between said intervals having a different trigger level, said different tRigger level being that wherein said normal non-alarm impedance places said trigger amplifier in an alarm preparatory state but does not operate said trigger amplifier.

Claim 6

A system according to claim 3, in which said test means comprises a periodically operating test circuit, and including test disabling means connecting said test circuit to said alarm signalling portion and responsive to detection of an alarm state by said detecting portion for rendering said test circuit inacting during said intervals, and indicating means in said detecting portion for indicating operation of the corresponding trigger amplifier.

Claim 7

A system according to claim 3 in which the impedance between the electrical conductors in the detecting means comprises the electrical transition resistance of a supporting material shunting the conductors, which together with the electrical conductors form the detecting means.

Claim 8

A system according to claim 5 in which the impedance between the electrical conductors in the detecting means comprising said transition resistance together with a bridging impedance member, connected between the electrical conductors.

Claim 9

A system according to claim 5 in which said material comprises a textile material impregnated with a substance sensitive to and activated by the vaporying state of liquids such that the transition resistance is changed between the electrical conductors.

Claim 10

A system according to claim 5 in which said material is impregnated with a substance sensitive to and actuated by heat such tht the transition resistance between the electrical conductors is changed upon heating.

Claim 11

A system according to claim 3 in which the test means is arranged to control in stages the level of amplification of said trigger amplifier during said intervals.

Claim 12

A system according to claim 9 in which said test means comprises pulse circuit means including timing means for producing pulses of length corresponding to said intervals and the ends of said periods separating said intervals, and a current path connecting said pulse circuit means to the input of said trigger amplifier in common with the connection of said detecting means thereto, whereby said pulses each produce said change of trigger level for the duration thereof.

Claim 13

A system according to claim 10 in which said test means further includes a fault indicator and elctronic switch means for actuating said fault indicator in the event of a fault in said detecting means and alarm state detecting portion, said test means further including switch disabling means connected between an output of said trigger amplifier and said electronic switch means (1) for disabling said electronic switch means and fault indicator upon production of an output signal from said trigger amplifier but (2) for permitting actuation of said fault indicator by said electronic switch means upon failure of said trigger amplifier to produce such output during said intervals.

Claim 14

A system according to claim 11 in which said disabling means comprises a thyristor gated on by said trigger amplifier output for blocking conduction of said electronic switch means and further including coupling means momentarily conductive at the onset of said pulse for momentarily disabling said thyristor, whereby failure of said trigger amplifier to produce said output thereof results in continuation of the disabled state of said thyristor during said interval, permitting said electronic switch means to actuate said fault indicator.

Claim 15

A system according to claim 11 including illuminated diode means connecting said output of said trigger amplifier to said switch disabling means for indicating operation of the corresponding trigger amplifier.

Claim 16

A system according to claim 10 in which said alarm signalling portion include a free running multivibrator and alternative alarm indicators coupled to opposite sides of said multivibrator for alternative actuation thereby upon detection of an alarm state, said trigger amplifier having a continuous supply output, means connecting said continuous supply output to a supply line of said multivibrator and responsive to actuation of said trigger amplifier for normally energizing said free running multivibrator, said trigger amplifier further having a pulse output energizeable at the time of initiation of trigger amplifier operation for a time period substantially corresponding to said interval, said alarm signalling portion including multivibrator disabling means coupled between said multivibrator and trigger amplifier pulse output (1) for disabling the former and thereby both said alternate alarm indicators during said intervals but (2) for permitting operation of said multivibrator to alternately actuate said alarm indicators in the presence of said trigger amplifier continuous supply output and absence of said trigger amplifier pulse output.

Claim 17

A system according to claim 14 in which said test means includes a fault indicator and indicator disabling means responsive to an output of said trigger amplifier during said intervals for disabling said fault indicator, said alarm signalling portion including alarm priority means responsive to energization of the multivibrator supply line and coupled to said fault indicator disabling means for then actuating the latter to disable said fault indicator, whereby an alarm is always given priority over and interrupts a fault indication.

Claim 18

A system according to claim 14 in which said timing means produces a pulse per said interval, said multivibrator supply line being coupled to said timing means for disabling same while an alarm state exists, to prevent changing of said trigger level of said trigger amplifier by said test means while an alarm state exists.

Claim 19

A system according to claim 14 including paralleling means for coupling several alarm state detecting portions in parallel to a single alarm signalling portion and test means, said alarm signalling portion including further multivibrator disabling means including a manual switch and means responsive to actuation of said manual switch for locking said multivibrator in one conductive state thereof, whereby one said alternate alarm indicators is energized and the other deenergized during an alarm state of one of said alarm state detecting portions, said paralleling means including means connecting the pulse output of another alarm signalling portion trigger amplifier through said first mentioned multivibrator disabling means for deactivating said further multivibrator disabling means, whereby if a second alarm is given during a first alarm state, said multivibrator will resume free running signal such second alarm state has occurred.